A passive SETI in globular clusters at the hydroxyl and water lines     

Nathaniel L. Cohen  Matthew A. Malkan  John M. Dickey 《Icarus》1980,41(2):198-204

We describe an indirect or “passive” SETI in 25 globular clusters, observed for astronomical reasons at the water and hydroxyl lines. No beacon signals were found in a sample of up to 10⁷ stars and upper limits to the maximum EIRPs of beacons were 10¹⁶–10²¹W. Ways of enhancing the value of other astronomical spectral line observing programs for SETI purposes are discussed.  相似文献   

A reevaluation of in situ cosmogenic 3He production rates     

Brent M. Goehring  Mark D. Kurz  Greg Balco  Joerg M. Schaefer  Joseph Licciardi  Nathaniel Lifton 《Quaternary Geochronology》2010,5(4):410-418

³He is among the most commonly measured terrestrial cosmogenic nuclides, but an incomplete understanding of the ³He production rate has limited robust interpretation of cosmogenic ³He concentrations. We use new measurements of cosmogenic ³He in olivine from a well-dated lava flow at Tabernacle Hill, Utah, USA, to calibrate the local ³He production rate. The new ³He measurements (n = 8) show excellent internal consistency and yield a sea level high latitude (SLHL) production rate of 123 ± 4 at g^?1 yr^?1 following the Lal (1991)/Stone (2000) scaling model [Lal, D., 1991. Cosmic ray labeling of erosion surfaces: in situ nuclide production rates and erosion models. Earth and Planetary Science Letters, 104, 424–439.; Stone, J.O., 2000. Air pressure and cosmogenic isotope production. Journal of Geophysical Research, 105, 23753–23759.]. We incorporate the new measurements from Tabernacle Hill in a compilation of all published production rate determinations, characterizing the mean global SLHL production rates (e.g. 120 ± 9.4 at g^?1 yr^?1 with Lal (1991)/Stone (2000)). The internal consistency of the global ³He production rate dataset is as good as the other commonly used cosmogenic nuclides. Additionally, ³He production rates in olivine and pyroxene agree within experimental error. The ³He production rates are implemented in an age and erosion rate calculator, forming a new module of the CRONUS-Earth web-based calculator, a simple platform for cosmogenic nuclide data interpretation [Balco, G., Stone, J., Lifton, N.A., and Dunai, T.J., 2008. A complete and easily accessible means of calculating surface exposure ages or erosion rates from ¹⁰Be and ²⁶Al measurements. Quaternary Geochronology, 3, 174–195.]. The ³He calculator is available online at http://www.cronuscalculators.nmt.edu/.  相似文献   

Long-term impact of the proglacial lake Jökulsárlón on the flow velocity and stability of Breiðamerkurjökull glacier,Iceland     

Nathaniel R. Baurley  Benjamin A. Robson  Jane K. Hart 《地球表面变化过程与地形》2020,45(11):2647-2663

Proglacial lakes are becoming ubiquitous at the termini of many glaciers worldwide due to continued climate warming and glacier retreat, and such lakes have important consequences for the dynamics and future stability of these glaciers. In light of this, we quantified decadal changes in glacier velocity since 1991 using satellite remote sensing for Breiðamerkurjökull, a large lake-terminating glacier in Iceland. We investigated its frontal retreat, lake area change and ice surface elevation change, combined with bed topography data, to understand its recent rapid retreat and future stability. We observed highly spatially variable velocity change from 1991 to 2015, with a substantial increase in peak velocity observed at the terminus of the lake-terminating eastern arm from ~1.00 ± 0.36 m day⁻¹ in 1991 to 3.50 ± 0.25 m day⁻¹ in 2015, with mean velocities remaining elevated from 2008 onwards. This is in stark comparison to the predominately land-terminating arms, which saw no discernible change in their velocity over the same period. We also observed a substantial increase in the area of the main proglacial lake (Jökulsárlón) since 1982 of ~20 km², equating to an annual growth rate of 0.55 km² year⁻¹. Over the same period, the eastern arm retreated by ~3.50 km, which is significantly greater than the other arms. Such discrepancies between the different arms are due to the growth and, importantly, depth increase of Jökulsárlón, as the eastern arm has retreated into its ~300 m-deep reverse-sloping subglacial trough. We suggest that this growth in lake area, forced initially by rising air temperatures, combined with the increase in lake depth, triggered an increase in flow acceleration, leading to further rapid retreat and the initiation of a positive feedback mechanism. These findings may have important implications for how increased melt and calving forced by climate change will affect the future stability of large soft-bedded, reverse-sloped, subaqueous-terminating glaciers elsewhere. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Hyper‐resolution global hydrological modelling: what is next?          下载免费PDF全文

Marc F. P. Bierkens  Victoria A. Bell  Peter Burek  Nathaniel Chaney  Laura E. Condon  Cédric H. David  Ad de Roo  Petra Döll  Niels Drost  James S. Famiglietti  Martina Flörke  David J. Gochis  Paul Houser  Rolf Hut  Jessica Keune  Stefan Kollet  Reed M. Maxwell  John T. Reager  Luis Samaniego  Edward Sudicky  Edwin H. Sutanudjaja  Nick van de Giesen  Hessel Winsemius  Eric F. Wood 《水文研究》2015,29(2):310-320

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Land use change effects on catchment streamflow response in a humid tropical montane cloud forest region,central Veracruz,Mexico     

Sergio M. López-Ramírez  Leonardo Sáenz  Alex Mayer  Lyssette E. Muñoz-Villers  Heidi Asbjornsen  Z. Carter Berry  Nathaniel Looker  Robert Manson  León Rodrigo Gómez-Aguilar 《水文研究》2020,34(16):3555-3570

Tropical montane cloud forests (TMCF) are recognized for their capacity to maintain high dry-season baseflow and a host of other ecosystem services. Substantial areas of TMCF have been converted to pasture and crops such as coffee, while in other areas TCMF are recovering. However, little is known about the effects of this complex dynamic on catchment hydrology. We investigated the effect of land use on rainfall-runoff response in five neighbouring headwater micro-catchments in central Veracruz, Mexico, dominated by either mature TMCF (MF), young (20 year-old) and intermediate (40 year-old) naturally regenerating TMCF (YF and IF, respectively), shaded coffee (SC), and an intensively grazed pasture (IP). We used a 4-year record of high-resolution rainfall and streamflow (10 min) data collected from 2015 to 2019. These data were analysed via comparison of hydrologic metrics that summarize streamflow responses at various time scales and magnitudes. Results showed no statistical difference in the regulation capacity of high flows in the micro-catchment with 20 years of natural regeneration, compared to the MF. In terms of baseflow sustenance, our results support the hypothesis that MF and IF better promote this hydrologic service than the other land uses. SC exhibited a high capacity to modulate peak flows comparable to that of MF, and an intermediate capacity to sustain baseflow, suggesting that the integrated functioning of this micro-catchment was largely preserved. Finally, 40 years of intense pasture management was found to have degraded the soil hydraulic properties of IP; mainly, reducing its infiltration capacity, causing a fivefold greater peak flow response and a lower baseflow compared to MF.  相似文献   

Quantification of the seasonal hillslope water storage that does not drive streamflow          下载免费PDF全文

David N. Dralle  W. Jesse Hahm  Daniella M. Rempe  Nathaniel J. Karst  Sally E. Thompson  William E. Dietrich 《水文研究》2018,32(13):1978-1992

The relationship between seasonal catchment water storage and discharge is typically nonunique due to water storage that is not directly hydraulically connected to streams. Hydraulically disconnected water volumes are often ecologically and hydrologically important but cannot be explicitly estimated using current storage–discharge techniques. Here, we propose that discharge is explicitly sensitive to changes in only some fraction of seasonally dynamic storage that we call “direct storage,” whereas the remaining storage (“indirect storage”) varies without directly influencing discharge. We use a coupled mass balance and storage–discharge function approach to partition seasonally dynamic storage between these 2 pools in the Northern California Coast Ranges. We find that indirect storage constitutes the vast majority of dynamic catchment storage, even at the wettest times of the year. Indirect storage exhibits lower variability over the course of the wet season (and in successive winter periods) than does direct storage. Predicted indirect storage volumes and dynamics match field observations. Comparison of 2 neighbouring field sites reveals that indirect storage volumes can occur as unsaturated storage held under tension in soils and weathered bedrock and as near‐surface saturated storage that remains on hillslopes (and is eventually evapotranspired). Indirect storage volumes (including moisture in the weathered bedrock) may support plant transpiration, and our method indicates that this important water source could be quantified from precipitation and stream discharge records.  相似文献   

HydroBlocks: a field‐scale resolving land surface model for application over continental extents          下载免费PDF全文

Nathaniel W. Chaney  Peter Metcalfe  Eric F. Wood 《水文研究》2016,30(20):3543-3559

Land surface spatial heterogeneity plays a significant role in the water, energy, and carbon cycles over a range of temporal and spatial scales. Until now, the representation of this spatial heterogeneity in land surface models has been limited to over simplistic schemes because of computation and environmental data limitations. This study introduces HydroBlocks – a novel land surface model that represents field‐scale spatial heterogeneity of land surface processes through interacting hydrologic response units (HRUs). HydroBlocks is a coupling between the Noah‐MP land surface model and the Dynamic TOPMODEL hydrologic model. The HRUs are defined by clustering proxies of the drivers of spatial heterogeneity using high‐resolution land data. The clustering mechanism allows for each HRU's results to be mapped out in space, facilitating field‐scale application and validation. The Little Washita watershed in the USA is used to assess HydroBlocks' performance and added benefit from traditional land surface models. A comparison between the semi‐distributed and fully distributed versions of the model suggests that using 1000 HRUs is sufficient to accurately approximate the fully distributed solution. A preliminary evaluation of model performance using available in situ soil moisture observations suggests that HydroBlocks is generally able to reproduce the observed spatial and temporal dynamics of soil moisture. Model performance deficiencies can be primarily attributed to parameter uncertainty. HydroBlocks' ability to explicitly resolve field‐scale spatial heterogeneity while only requiring an increase in computation of one to two orders of magnitude when compared with existing land surface models is encouraging – ensemble field‐scale land surface modelling over continental extents is now possible. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Prediction and assimilation of surf-zone processes using a Bayesian network: Part II: Inverse models     

Nathaniel G. Plant  K. Todd Holland 《Coastal Engineering》2011

A Bayesian network model has been developed to simulate a relatively simple problem of wave propagation in the surf zone (detailed in Part I). Here, we demonstrate that this Bayesian model can provide both inverse modeling and data-assimilation solutions for predicting offshore wave heights and depth estimates given limited wave-height and depth information from an onshore location. The inverse method is extended to allow data assimilation using observational inputs that are not compatible with deterministic solutions of the problem. These inputs include sand bar positions (instead of bathymetry) and estimates of the intensity of wave breaking (instead of wave-height observations). Our results indicate that wave breaking information is essential to reduce prediction errors. In many practical situations, this information could be provided from a shore-based observer or from remote-sensing systems. We show that various combinations of the assimilated inputs significantly reduce the uncertainty in the estimates of water depths and wave heights in the model domain. Application of the Bayesian network model to new field data demonstrated significant predictive skill (R² = 0.7) for the inverse estimate of a month-long time series of offshore wave heights. The Bayesian inverse results include uncertainty estimates that were shown to be most accurate when given uncertainty in the inputs (e.g., depth and tuning parameters). Furthermore, the inverse modeling was extended to directly estimate tuning parameters associated with the underlying wave-process model. The inverse estimates of the model parameters not only showed an offshore wave height dependence consistent with results of previous studies but the uncertainty estimates of the tuning parameters also explain previously reported variations in the model parameters.  相似文献   

A Bayesian approach to calibrating period-luminosity relations of RR Lyrae stars in the mid-infrared     

Christopher R. Klein  Joseph W. Richards  Nathaniel R. Butler  Joshua S. Bloom 《Astrophysics and Space Science》2012,341(1):83-87

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College students’ consumption, contribution, and risk awareness related to online mapping services and social media outlets: does geography and GIS knowledge matter?     

Adam J. Mathews  Yongmei Lu  Matthew T. Patton  Nathaniel Dede-Bamfo  Junfang Chen 《GeoJournal》2013,78(4):627-639

Location-enabled online tools and/or services (i.e. Google Earth/Maps, Flickr, Facebook check-ins, etc.) have been widely used for distributing and processing geospatial-related data. They attract diverse users to consume and contribute geographic information (GI) in many different forms. This study examines college students’ consumption and contribution of GI through these tools and/or services as well as their perception of risk and privacy. It evaluates the impact of Geographic information systems (GIS) and geography knowledge on the related behavior and perception. Through conducting a survey, it was found that college students’ consumption frequency of GI through the investigated tools and services is positively related to their knowledge in GIS and geography, but their GI contribution is not related. GIS knowledge was found to help raise students’ awareness level of risk. However, this relationship does not translate into students’ concern about potential privacy disclosure or their willingness to share personal location information through using location-enabled online tools and/or services. Discussions on the gap between students’ consumption and contribution of GI through the tools and/or services are shared in the paper as well as possible explanations on the disconnection between their risk awareness, privacy concern, and willingness to share personal information. Future research directions are discussed.  相似文献